The invention relates to cranes and like load raising, lowering and transferring machines, and more particularly to improvements in swivels for use in cranes or the like. Still more particularly, the invention relates to improvements in swivels which can be used in cranes and analogous machines to permit untangling of load-carrying flexible elements in the form of bands, cords, wires, cables or ropes (hereinafter called cables).
As used in the field of cranes, derricks, elevators, hoists, winches and like machines, the term swivel denotes a combination of two members one of which is acted upon by pull and can turn relative to the other member about an axis which coincides with the direction of pull. If the swivel is used in a crane, the other member is fixedly or articulately connected to the frame of the crane (e.g., to the boom) and one end of the cable is connected with the one member. The one end of the cable applies a load to the one member, and such one end of the cable can turn with the one member relative to the other member, for example, in order to relieve the cable of torsional or twisting stresses.
The cable of a crane is likely to be subjected to torsional stresses by the cable drum in normal use of the crane, particularly by a cable drum which is designed to store several layers of convoluted cable. For example, torsional stresses will develop if the idler rollers are not accurately aligned with the cable. This entails a twisting of the cable and the development of undesirable torsional stresses. If the cable which is connected with the one member of the swivel is looped, and the bight of its loop carriers a dancer roll for a crane hook or another load carrying structure, twisting is likely to take place in that part of the cable which extends from the dancer roll toward the cable drum. Thus, even though that portion of the cable which extends between the dancer roll and the one member of the swivel is less likely to be twisted, torsional stresses acting upon the other portion of the cable (between the dancer roll and the cable drum) are often sufficiently pronounced to cause a change of orientation of the dancer roll and a crossing of cable portions which flank the dancer roll. Such crossing is particularly likely to take place if the cable is long, i.e., if the load carrying structure on the dancer roll is called upon to raise or lower a load through a considerable distance. Crossing of cable portions which flank the load carrying parts is undesirable because the two portions of the cable rub against each other and the load is likely to turn during raising or lowering.